We investigate electron and phonon transport through edge disordered zigzag graphene nanoribbons based on the same methodological tool of nonequilibrium Green functions. We show that edge disorder dramatically reduces phonon thermal transport while being only weakly detrimental to electronic conduction. The behavior of the electronic and phononic elastic mean free paths points to the possibility of realizing an electron-crystal coexisting with a phonon-glass. The calculated thermoelectric figure of merit (ZT) values qualify zigzag graphene nanoribbons as a very promising material for thermoelectric applications. Still, ab initio calculations of thermoelectric phenomena for larger systems is bottlenecked by the extremely computational demanding algorithms employing nonequilibrium Green function approaches. To cope with this known problem, we can show first results of a methodological implementation outperforming nonequilibrium Green functions. First benchmarks of this order $N$ new method based on the time dependent propagation of phonon wave-packets in real space show the up-scalability of the calculations of the thermal conductance in large sized edge disordered graphene nanoribbons. Applications for molecular thermoelectrics will also be presented.